Acoustic emission testing is a technique for accessing structural integrity. The presence of flaws in pressure vessels can be detected with this technique. Acoustic sensors are affixed to the pressure vessel wall, and are connected to a signal processor. When the vessel is pressurized, flaws will produce stress wave emission. The stress waves will propagate throughout the vessel and passage of stress waves will be detected by the sensors.
A problem associated with acoustic emission testing is the generation of acoustic emission events caused, not by structural flaws within the vessel, but by the action of pressurizing fluid. Secondary flows impinge upon the inside walls of the pressure vessel and may produce noise which affects the sensors. Such flow noise may produce acoustic emission data in addition to that produced by flaws. There are some conventional ways to eliminate flow noise but these conventional methods have severe disadvantages.
One way of addressing the flow noise problem is to pressurize the vessel to the target pressure at a low flow rate thus reducing or completely eliminating secondary flows and hence the noise problem. However this method is disadvantageous because of the consequent long time it takes to pressurize the vessel to the desired pressure. This time problem is especially severe when there are a large number of pressure vessels which must undergo testing.
Another way of addressing the flow noise problem is to set a high threshold on the acoustic emission signal processor so that the signals associated with secondary flows are below the threshold. This has the unfavorable result of the failure to record low amplitude structural emission.
It is therefore an object of this invention to provide a method for carrying out acoustic emission testing of a pressure vessel in an elapsed time faster than heretofore possible while reducing inaccuracy of test data due to flow noise from the pressurizing fluid and/or to a high threshold on the acoustic emission signal processor.